Surface emission device, optical element and liquid crystal display device

ABSTRACT

Using a distance L between the centers of light sources  12, 12 ; a refractive index n of an optical element  15 ; a thickness d of the optical element; a distance W from the center of the light source to the optical element; a refractive index n 0  of air; an angle of incidence θ 1  of light emitted from the light sources and coming into the optical element, relative to the direction of optical axes; an angle of refraction θ 2  of light, incident on the optical element, in the optical element; a diameter of each light source as D; and a maximum tangential angle a formed between a tangential line in contact with an outer surface of a luminance distribution generating layer  18  and a plane orthogonal to the optical axes, there is included a maximum tangential angle a satisfying x&gt;L/2−D/2 when calculating a travel range x of a split image of the light sources in a direction normal to the optical axes using (1) n 0  sin(a)=n sin(a−θ 2 ), (2) n 0  sin θ 1 =n sin θ 2  and (3) x=W tan θ 1 +d tan θ 2 . This facilitates uniformalizing of front luminance distribution.

TECHNICAL FIELD

The present invention relates to technical fields of surface emissiondevice, optical element and liquid crystal display device. For moredetail, the present invention relates to technical fields of suppressingnon-uniformity in luminance by allowing split images of light sources tooverlap between the light sources.

BACKGROUND ART

Liquid crystal display devices provided with backlight (surface emissiondevice) have conventionally been used as display devices for wordprocessors, laptop personal computers and so forth. As the surfaceemission device for this type of liquid crystal display devices, anedge-light-type backlight, having linear light sources just likefluorescent lamps disposed laterally on a transparent plate (light guideplate), in response to demands for weight reduction and thinning, hasbeen in the main stream.

The edge-light-type backlight has, however, often resulted ininsufficient luminance with recent expansion in size of the liquidcrystal display device represented by those used for television sets, sothat a direct-type backlight, having linear light sources arrangedstraightly under the liquid crystal display panel has more widely beenadopted.

FIG. 32 is a perspective view showing a schematic configuration of aconventional direct-type backlight unit 1. The backlight unit 1 haslight sources (linear light sources) 2, 2, . . . such as fluorescentlamps, a reflective plate 3, and a diffuser plate 4.

As the light sources (linear light sources) 2, 2, . . . , cold cathodefluorescent lamps (CCFL) or the like are used, which are formed intocolumns extended in a predetermined direction.

The reflective plate 3 is disposed so as to make use, in a recycledmanner, of light reflected on the diffuser plate 4, etc., or lightemitted from the light sources 2, 2, . . . , but not reached thediffuser plate 4.

The diffuser plate 4 is an optical element of at least 1 mm thick ormore improved in diffusing and scattering performances, by virtue ofhaving a transparent base and a resin component different from thetransparent base in the refractive index randomly contained therein, andis used as an optical element for suppressing variation in frontluminance distribution.

In the backlight unit 1, the reflective plate 3 and the diffuser plate 4are disposed respectively on both sides of the light sources 2, 2, . . ..

In thus-configured backlight unit 1, light emitted from the lightsources 2, 2, . . . is extracted from the diffuser plate 4, whereinluminance of illumination flux of the backlight unit 1 may be highstraightly above the light sources 2, 2, . . . and may be low betweenthe light sources 2, 2, . . . as shown in FIG. 33, when the distancebetween the light sources 2, 2, . . . and the diffuser plate 4 becomessmall, or the distance between the individual light sources 2, 2, . . .becomes large, and this may degrade uniformity in the front luminancedistribution and may cause variation in luminance.

In order to suppress such variation in luminance, as shown in FIG. 34,there has been known a technique of disposing an optical sheet (opticalelement) 5 such as prism sheet or lenticular lens sheet between thelight sources 2, 2, . . . and the diffuser plate 4, or disposing anoptical sheet (optical element) 5 such as prism sheet or lenticular lenssheet in place of the diffuser plate 4 (see Japanese Patent ApplicationPublication (KOKAI) Nos. H5-333333, H6-250178, H10-283818, and2004-6256). FIG. 34 shows an exemplary case where the optical element(prism sheet) 5 is disposed in place of the diffuser plate 4 shown inFIG. 33.

The optical element (prism sheet) 5 has, on the front surface or theback surface thereof, a plurality of linear projections (prisms)consecutively provided at regular pitches, typically having a triangleprofile, and is an optical element generally adopted as a sheet forimproving luminance. These linear projections function as a luminancedistribution generating layer 5 a which suppresses variation inluminance in the direction of optical axes of light emitted from thelight sources 2, 2, . . . .

The optical element 5 is disposed so that the direction of ridge of thelinear projections which function as a luminance distribution generatinglayer 5 a agrees with the longitudinal direction of the light sources 2,2, . . . . By using the optical element 5, as shown in FIG. 34,extracted illumination flux is split into a plurality of fluxes to givesplit images 2A, 2A, . . . of each light source, and thereby thevariation in the front luminance distribution may be suppressed. FIG. 34shows an exemplary case where the number of split images 2A, 2A, . . .of each light source was doubled from the number of the light sources 2,2, . . . by the optical element 5.

DISCLOSURE OF THE INVENTION

The above-described conventional surface emission device 1 has, however,been suffering from a problem in that a large non-uniformity inluminance is likely to occur, when the distance between the lightsources 2, 2, . . . and the optical element 5 varies. Variation in thedistance may be ascribable to accuracy in processing or assembling ofthe individual components, or to deformation of the optical element dueto environmental changes such as changes in temperature.

For example, as shown in FIG. 35, in a surface emission device designedto ensure uniform front luminance distribution with respect to each ofthe split images 2A, 2A, . . . of the light sources 2, 2, . . . , whenthe distance between the centers of the light sources 2, 2, . . . andthe optical element 5 is given as H, a change in the designed distance Hof the optical element 5 to as much as ΔH may be highly causative ofnon-uniformity in luminance as shown in FIG. 36.

The surface emission device 1 is designed so as avoid overlapping of onesplit image 2A of the light source 2 with the adjacent split image 2A ofthe light source 2, so far as the designed distance H is maintained, sothat such non-uniformity in luminance may occur as a result of a sharpchange in the front luminance distribution when the distance H varies.More specifically, a change in the distance H to as much as ΔH may causeoverlapping of the split images 2A, 2A, . . . of the individual lightsources 2, 2, . . . , and may raise a sharp change in the frontluminance distribution, making non-uniformity in luminance more likelyto occur.

The distance between the light sources 2, 2, . . . and the opticalelement 5 is therefore designed so that a uniform front luminancedistribution, as shown in FIG. 35, may be obtainable, but only with asmall degree of freedom in the design.

On the other hand, with recent trends in expansion in size of the liquidcrystal display devices, also the surface emission devices (backlightunit) have been expanded in size. As a consequence, also the opticalelements such as prism sheet, lenticular sheet and so forth are to beexpanded in size, for the purpose of making the front luminancedistribution uniform.

Expansion in size of these optical elements, however, makes them morelikely to cause sagging or warping due to their self weight, and makesit difficult to stably and uniformly maintain the distance between theoptical element and the light sources over the entire surface of theoptical element. As a consequence, variation in the distance may becaused between the optical element and the light sources as shown inFIG. 36, the front luminance distribution may be prevented from beingmade uniform, and non-uniformity in luminance may be more likely tooccur.

It is therefore a subject of a surface emission device, an opticalelement and a liquid crystal display device of the present invention toovercome the above-described problems, and to suppress non-uniformity inluminance by ensuring uniformity in the front luminance distribution,even when the distance between the light sources and the optical elementshould vary.

Aiming at solving the above-described problems, a surface emissiondevice, an optical element and a liquid crystal display device of thepresent invention is configured as containing a maximum tangential anglea which satisfies x>L/2−D/2, when travel range x of a split image of thelight sources in the direction orthogonally crossing the optical axes iscalculated using (1) n₀ sin(a)=n sin(a−θ₂), (2) n₀ sin θ₁=n sin θ₂, and(3) x=W tan θ₁+d tan θ₂, assuming distance between the centers of everyadjacent light sources as L; refractive index of the optical element asn; thickness of the optical element as d; distance from the center ofthe light sources to the optical element in the direction of opticalaxes as W; refractive index of air in the air layer as n₀; angle ofincidence of light emitted from the light sources and coming into theoptical element, relative to the direction of optical axes, as θ₁; angleof refraction of light, incident on the optical element, in the opticalelement as θ₂; diameter of the light source as D; angles formed betweena tangential line in contact with the outer surface of the luminancedistribution generating layer and a plane orthogonal to the opticalaxes, as viewed in a sectional profile orthogonal to the longitudinaldirection of the structural portions of the luminance distributiongenerating layer, as tangential angles ψ; and a tangential angle largestof all tangential angles ψ as maximum tangential angle a.

Accordingly, in the surface emission device, the optical element and theliquid crystal display device, at least part of the split images of theindividual light sources positioned adjacent to each other may beoverlapped.

The surface emission device of the present invention is a surfaceemission device having a plurality of light sources respectively shapedinto a columnar form extending in a predetermined direction and disposedon the same plane as being extended in the same direction; an opticalelement having transparency and having, as formed therein, a luminancedistribution generating layer suppressing variation, in the direction ofoptical axes, in luminance of light emitted from the plurality lightsources; and a reflective surface positioned as being opposed to theoptical element across the plurality of light sources, while keeping anair layer between the optical element and itself, and reflecting lightemitted from the light sources, wherein the luminance distributiongenerating layer of the optical element being composed of a plurality ofstructural portions extending in the longitudinal direction of the lightsources and projecting in the direction of optical axes. The surfaceemission device is characterized by, assuming distance between thecenters of every adjacent light sources as L; refractive index of theoptical element as n; thickness of the optical element as d; distancefrom the center of the light sources to the optical element in thedirection of optical axes as W; refractive index of air in the air layeras n₀; angle of incidence of light emitted from the light sources andcoming into the optical element, relative to the direction of opticalaxes, as θ₁; angle of refraction of light, incident on the opticalelement, in the optical element as θ₂; diameter of each light source asD; angles formed between a tangential line in contact with the outersurface of the luminance distribution generating layer and a planeorthogonal to the optical axes, as viewed in a sectional profileorthogonal to the longitudinal direction of the structural portions ofthe luminance distribution generating layer, as tangential angles ψ; anda tangential angle largest of all tangential angles ψ as maximumtangential angle a; having the optical element containing the maximumtangential angle a which satisfies x>L/2−D/2, when travel range x of asplit image of the light sources in the direction normal to the opticalaxes is calculated using the conditional equation (1) to conditionalequation (3) below.

n ₀ sin(a)=n sin(a−θ ₂)  (1)

n₀ sin θ₁=n sin θ₂  (2)

x=W tan θ₁ +d tan θ₂  (3)

The optical element of the present invention is an optical element beingconfigured as having formed therein a luminance distribution generatinglayer suppressing variation, in the direction of optical axes, inluminance of light emitted from the plurality light sources respectivelyshaped into a columnar form extending in a predetermined direction anddisposed on the same plane as being extended in the same direction,wherein the luminance distribution generating layer is composed of aplurality of structural portions extending in the longitudinal directionof the light sources and projecting in the direction of optical axes.The optical element is characterized by being, assuming distance betweenthe centers of every adjacent light sources as L; refractive index ofthe optical element as n; thickness of the optical element as d;distance from the center of the light sources to the optical element inthe direction of optical axes as W; refractive index of air in the airlayer as n₀; angle of incidence of light emitted from the light sourcesand coming into the optical element, relative to the direction ofoptical axes, as θ₁; angle of refraction of light, incident on theoptical element, in the optical element as θ₂; diameter of each lightsource as D; angles formed between a tangential line in contact with theouter surface of the luminance distribution generating layer and a planeorthogonal to the optical axes, as viewed in a sectional profileorthogonal to the longitudinal direction of the structural portions ofthe luminance distribution generating layer, as tangential angles ψ; anda tangential angle largest of all tangential angles ψ as maximumtangential angle a; configured so as to contain the maximum tangentialangle a which satisfies x>L/2−D/2, when travel range x of a split imageof the light sources in the direction normal to the optical axes iscalculated using the conditional equation (1) to conditional equation(3) below.

n ₀ sin(a)=n sin(a−θ ₂)  (1)

n₀ sin θ₁=n sin θ₂  (2)

x=W tan θ₁ +d tan θ₂  (3)

The liquid crystal display device is a liquid crystal display devicehaving a plurality of light sources respectively shaped into a columnarform extending in a predetermined direction and disposed on the sameplane as being extended in the same direction; an optical element havingtransparency and having, as formed therein, a luminance distributiongenerating layer suppressing variation, in the direction of opticalaxes, in luminance of light emitted from the plurality light sources,the luminance distribution generating layer being composed of aplurality of structural portions extending in the longitudinal directionof the light sources and projecting in the direction of optical axes; areflective surface positioned as being opposed to the optical elementacross the plurality of light sources, while keeping an air layerbetween the optical element and itself, and reflecting light emittedfrom the light sources; and a liquid crystal panel allowing thereonimage display and irradiated with light emitted from the plurality oflight sources. The liquid crystal display device is characterized by,assuming distance between the centers of every adjacent light sources asL; refractive index of the optical element as n; thickness of theoptical element as d; distance from the center of the light sources tothe optical element in the direction of optical axes as W; refractiveindex of air in the air layer as n₀; angle of incidence of light emittedfrom the light sources and coming into the optical element, relative tothe direction of optical axes, as θ₁; angle of refraction of light,incident on the optical element, in the optical element as θ₂; diameterof each light source as D; angles formed between a tangential line incontact with the outer surface of the luminance distribution generatinglayer and a plane orthogonal to the optical axes, as viewed in asectional profile orthogonal to the longitudinal direction of thestructural portions of the luminance distribution generating layer, astangential angles ψ; and a tangential angle largest of all tangentialangles ψ as maximum tangential angle a; having the optical elementcontaining the maximum tangential angle a which satisfies x>L/2−D/2,when travel range x of a split image of the light sources in thedirection normal to the optical axes is calculated using the conditionalequation (1) to conditional equation (3) below.

n ₀ sin(a)=n sin(a−θ ₂)  (1)

n₀ sin θ₁=n sin θ₂  (2)

x=W tan θ₁ +d tan θ₂  (3)

Accordingly, in the surface emission device, the optical element and theliquid crystal display device of the present invention, at least part ofthe split images of the individual light sources positioned adjacent toeach other may be overlapped, so that the front luminance distributionis ensured with a desirable level of uniformity, and thereby thenon-uniformity in luminance may be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view showing, together with FIG. 2 toFIG. 31, a best mode for embodying a surface emission device, opticalelement and liquid crystal display device of the present invention, inwhich this drawing shows a liquid crystal display device.

FIG. 2 is a conceptual drawing showing positional relation and so on ofroute of light emitted from light sources and the individual components.

FIG. 3 is a conceptual drawing showing a tangential angle at astructural portion of a luminance distribution generating layer.

FIG. 4 is a graph showing a front luminance distribution observed in astate where light is emitted from a single light source.

FIG. 5 is a conceptual drawing showing, together with FIG. 6 and FIG. 7,an exemplary front luminance distribution, wherein this drawing showsthat having a near-triangle profile with a rounded apex.

FIG. 6 is a conceptual drawing showing an example having shoulders onthe inclined portions thereof.

FIG. 7 is a conceptual drawing showing an example having step-wiselyvaried slope on the inclined portions.

FIG. 8 is a graph showing front luminance distribution of light beforetransmitting a diffuser plate, under varied distance between the lightsource and the optical element.

FIG. 9 is a graph showing front luminance distribution of light beforetransmitting a diffuser plate, under varied distance between the lightsource and the optical element, for a case where split images of thelight source slightly overlap.

FIG. 10 is a conceptual drawing showing a specific example of travelrange of the split image of the light source, in the direction normal tothe optical axes of the light sources.

FIG. 11 is a graph showing a relation between tangential angle of theluminance distribution generating layer and travel range of the splitimage of the light source.

FIG. 12 is a graph showing a front luminance distribution observed whenthe split image of the light source moves to the adjacent light source.

FIG. 13 is a graph showing a relation between the maximum tangentialangle of the luminance distribution generating layer and the travelrange of split image of the light source.

FIG. 14 is a graph showing a front luminance distribution in a statewhere light emitted from the light source is transmitted through thediffuser plate, when the light source and the optical element keep adesigned distance therebetween.

FIG. 15 is a graph showing a front luminance distribution in a statewhere light emitted from the light source transmitted through thediffuser plate, when the split images of the light source slightlyoverlap, and when the light source and the optical element keep adesigned distance therebetween.

FIG. 16 is a graph showing tangential angle and its ratio for sampleshaving small incidence of non-uniformity in luminance.

FIG. 17 is a graph showing tangential angle and its ratio for sampleshaving large incidence of non-uniformity in luminance.

FIG. 18 is a graph showing a front luminance distribution observed in astate where light emitted from a plurality of light sources istransmitted through the optical element.

FIG. 19 is a conceptual drawing showing an example of the structuralportion of the luminance distribution generating layer.

FIG. 20 is a graph showing tangential angle and its ratio, for theluminance distribution generating layer shown in FIG. 19.

FIG. 21 is a graph showing a front luminance distribution in a statewhere light emitted from the light sources is transmitted through thediffuser plate, for the cases shown in FIG. 19 and FIG. 20.

FIG. 22 is a conceptual drawing showing an optical element packagehaving the optical element, the diffuser plate and an optical elementcomponent packaged by a packaging component.

FIG. 23 is a conceptual drawing showing an optical element packagehaving the optical element and the diffuser plate bonded to each other.

FIG. 24 is a drawing showing an exemplary luminance distributiongenerating layer having a polygonal profile.

FIG. 25 is a drawing showing an exemplary luminance distributiongenerating layer having structural portions having two polygonalprofiles.

FIG. 26 is a drawing showing another exemplary luminance distributiongenerating layer having structural portions having two polygonalprofiles.

FIG. 27 is a drawing showing an optical element having the structuralportion having two polygonal profiles, and a die for molding the opticalelement.

FIG. 28 is a drawing showing an exemplary luminance distributiongenerating layer having structural portions having three polygonalprofiles.

FIG. 29 is a drawing showing another exemplary luminance distributiongenerating layer having structural portions having three polygonalprofiles.

FIG. 30 is a drawing showing results of simulation of front luminancedistribution observed when only one light source in the optical elementhaving the luminance distribution generating layer shown in FIG. 26 islit.

FIG. 31 is a drawing showing results of simulation of front luminancedistribution observed when all light sources in the optical elementhaving the luminance distribution generating layer shown in FIG. 26 areturned on.

FIG. 32 is a schematic sectional view showing a conventional surfaceemission device.

FIG. 33 is a conceptual drawing showing an exemplary front luminancedistribution observed under shortened distance between the light sourceand the diffuser plate in a conventional surface emission device.

FIG. 34 is a conceptual drawing showing an exemplary front luminancedistribution in a conventional surface emission device.

FIG. 35 is a conceptual drawing showing an exemplary front luminancedistribution observed when the light source and the optical element aredisposed at a designed distance in a conventional surface emissiondevice.

FIG. 36 is a conceptual drawing explaining problems in the conventionalsurface emission device.

BEST MODES FOR CARRYING OUT THE INVENTION

Paragraphs below will explain best modes for carrying out the surfaceemission device, the optical element and the liquid crystal displaydevice of the present invention, referring to the attached drawings.

A surface emission device 10 is used as a direct-type backlight unitadapted to a liquid crystal display device 50 (see FIG. 1).

The surface emission device 10 has the individual components disposed ina housing 11, and is provided with a plurality of light sources (linearlight sources) 12, 12, . . . , a reflective plate 13, a diffuser plate14, an optical element (optical plate) 15 and an optical elementcomponent 16.

As the light sources 12, 12, . . . , fluorescent lamps such as coldcathode fluorescent lamps or hot cathode fluorescent lamps are adopted.The light sources 12, 12, . . . are respectively shaped into a columnarform, and are disposed on the reflective plate 13 as being extended inthe Y-direction shown in FIG. 1. The light sources 12, 12, . . . aredisposed at regular intervals in the X-direction shown in FIG. 1,between the reflective plate 13 and the optical element 15.

In the surface emission device 10, since a plurality of light sources12, 12, . . . are disposed at regular intervals on the reflectivesurface 13 a so as to ensure uniformity in the state of arrangement asshown in the above, so that light emitted from the light sources 12, 12,. . . is less likely to cause partial non-uniformity in luminancedepending on the state of arrangement of the light sources 12, 12, . . .when it reaches a liquid crystal display panel described later.

The surface of the reflective plate 13 opposed to the light sources 12,12, . . . is formed as the reflective surface 13 a. Part of lightemitted from the light sources 12, 12, . . . is reflected on thereflective surface 13 a back to the optical element 15. The reflectiveplate 13 may be anything so far as it has a property of reflectinglight, allowing use of a variety of those composed of aluminum, PET(polyethylene terephthalate), polycarbonate and so forth.

The diffuser plate 14 is disposed as being opposed to the light sources12, 12, . . . across the optical element 15. The diffuser plate 14 has afunction of diffusing light transmitted through the optical element 15and uniformalizing a luminance distribution of the illumination fluxemitted in the front direction, that is, front luminance distribution.Alternatively, in the surface emission device 10, also a thin diffusersheet may be adoptable in place of the diffuser plate 14.

As the diffuser plate 14, those composed of polystyrene, cycloolefinpolymer, acryl and polycarbonate may typically be used, whereas as thediffuser sheet, those capable of assisting diffusion of light, such ashaving filler particles coated on a PET base, may be used. Note that,although it is good enough to use at least either one of the diffuserplate 14 and diffuser sheet, they may be used in a stacked manner.

On the light extraction surface side of the diffuser plate 14, a liquidcrystal display panel is disposed although not shown.

The optical element 15 is disposed between the light sources 12, 12, . .. and the diffuser plate 14. The optical element 15 is typically a prismsheet or a lenticular lens sheet having transmissivity of light, and isconfigured with a luminance distribution generating layer 18 formed onthe light extraction surface side of a base 17 as being integratedtherewith.

The base 17 is formed using a plate material made of a transparentsynthetic resin such as acrylic resin, polyethylene terephthalate,polyethylene naphthalate, polycarbonate, styrene-base resin,styrene-methyl methacrylate copolymer resin and so forth. Note that,although the base 17 may alternatively be configured in a form of sheetor film, formation using a highly rigid plate material may be morepreferable, because such base 17 may be less likely to sag, warp ordeform by heat when incorporated into the housing 11, and less likely tovary the distance between the light source 12 and itself in theZ-direction. Thickness of the base 17 is not specifically limited, andeven the thickness as small as that of sheet or film may be allowable sofar as a predetermined rigidity may be ensured.

The luminance distribution generating layer 18 functions as suppressingvariation in luminance in the front direction (Z-direction) of lightemitted from the light sources 12. The luminance distribution generatinglayer 18 is configured with a plurality of structural portions 18 a, 18a, . . . , having the direction of ridges thereof agreed with theY-direction shown in FIG. 1, and the structural portions 18 a, 18 a, . .. are consecutively disposed in the X-direction at predeterminedpitches. Each structural portion 18 a is made project toward theZ-direction shown in FIG. 1, that is, the direction of optical axis oflight emitted from the light source 12, and has an outer surface thereoftypically formed into a curved profile or polygonal profile. Thestructural portion 18 a formed into the curved profile may have anaspherical profile, for example.

Pitch of arrangement of the structural portions 18 a, 18 a, . . . isirrespective of the pitch of arrangement of the light sources 12, 12, .. . , wherein the structural portions 18 a, 18 a, . . . are arranged atmicro pitches.

The luminance distribution generating layer 18 may be formed as beingintegrated with the base 17, but may be formed by transferring theluminance distribution generating layer 18 formed using a UV-curableresin onto the base 17, or may be formed by bonding the luminancedistribution generating layer 18 to the base 17 by press forming.

The optical element component 16 is composed of one of, or a pluralityof various optical elements such as diffuser sheet, prism sheet andreflective polarizer. For a case where the optical element component 16is composed of a plurality of optical elements, these plurality ofoptical elements are disposed as being stacked. The optical elementcomponent 16 is disposed as being opposed to the optical element 15across the diffuser plate 14.

In thus-configured surface emission device 10, a space between thereflective plate 13 and the optical element 15 is formed as an air layer19.

In the surface emission device 10, once the light is emitted from thelight sources 12, 12, . . . , the emitted light sequentially transmitsthe optical element 15, the diffuser plate 14 and the optical elementcomponent 16, and is irradiated onto the liquid crystal display panel.Part of the emitted light herein is reflected on the reflective surface13 a of the reflective plate 13, and is directed to the optical element15.

The light incident on the optical element 15 is refracted on the planeof incidence of the optical element 15, and is again refracted also whenit is emitted out from the optical element 15, and is then directed tothe diffuser plate 14. The light incident on the diffuser plate 14 isextracted therefrom after being diffused, transmits through the opticalelement component 16, and reaches the liquid crystal display panel.

FIG. 2 shows positional relations of route of light emitted from thelight sources 12, 12, . . . and the individual components.

In FIG. 2, distance between the centers of every adjacent light sources12, 12 is given as L, refractive index of the optical element 15 isgiven as n, thickness of the optical element 15 is given as d, distancefrom the center of the light source 12 to the optical element 15 in thedirection of optical axes P is given as W, refractive index of air inthe air layer 19 is given as n₀, angle of incidence of light emittedfrom the light source 12 and coming into the optical element 15,relative to the direction of optical axes P, is given as θ₁, angle ofrefraction of light, incident on the optical element 15, in the opticalelement 15 is give as θ₂, and diameter of the light source 12 is givenas D.

It is noted that FIG. 2 shows the size of the structural portions 18 a,18 a, . . . of the luminance distribution generating layer 18 as beingemphasized with respect to the base 17 of the optical element 15, andthat actual size of the structural portions 18 a, 18 a, is extremelysmaller than that of the base 17.

In addition, as shown in FIG. 3, in a sectional profile orthogonal tothe longitudinal direction of the structural portions 18 a, 18 a, . . .of the luminance distribution generating layer 18, an angle formedbetween a tangential line S in contact with the outer surface of thestructural portion 18 a and a plane Q orthogonal to the optical axis Pis given as tangential angle ψ. In this case, as shown in FIG. 2, atangential angle largest of all tangential angles ψ is given as maximumtangential angle a, and travel range of a split image 12A of the lightsource 12 in the direction normal to the optical axis P from the lightsource 12 is given as x. The travel range x represents a distance fromthe end face of the light source 12.

Using these factors (parameters), in the surface emission device 10, theequation (1) to equation (3) is held.

n ₀ sin(ψ)=n sin(ψ−θ₂)  (1)

n₀ sin θ₁=n sin θ₂  (2)

x=W tan θ₁ +d tan θ₂  (3)

With these equation (1) to equation (3), substituting an arbitrarytangential angle ψ in the equation (1) yields the angle of refractionθ₂, substituting the calculated θ₂ in the equation (2) yields the angleof incidence θ₁, and substituting the calculated θ₁ and θ₂ in theequation (3) yields the travel range x. As a consequence, the travelrange x corresponding to the tangential angle ψ is unconditionallydetermined, and a split image 12A of light reached the point of contactof the luminance distribution generating layer 18 having the tangentialangle ψ is shifted towards the adjacent light source 12 to as much as x.

As described in the above, the travel range x of the split image 12A isdetermined by the tangential angle Ψ, and assuming now that a tangentialangle, out of all tangential angles ψ, under which the split image 12Aof the light source 12 reaches L/2 is given as b, and a tangentialangle, out of all tangential angles ψ, under which the split image 12Aof the light source 12 reaches L, that is, the center of the adjacentlight source 12, is given as c, tangential angle ψ satisfying

x=L/2−D/2  (4)

equals tangential angle b. (L/2−D/2) stands for the middle positionbetween the individual centers of the adjacent light sources 12, 12.Accordingly, if any tangential angle ψ satisfying the equation (5) belowshould reside, the individual split images 12A, 12A of the adjacentlight sources 12, 12 should overlap:

x>L/2−D/2  (5).

As described in the above, presence of tangential angle ψ satisfying theequation (5) means overlapping of the individual split images 12A, 12Aof the adjacent light sources 12, 12, and this means that, if themaximum tangential angle a, allowing thereunder the equation (5) tohold, should reside in the luminance distribution generating layer 18,the individual split images 12A, 12A of the adjacent light sources 12,12 may overlap.

In the surface emission device 10, the optical element 15 is formed sothat the maximum tangential angle a, allowing thereunder the equation(5) to hold, may reside in the luminance distribution generating layer18, and so that the individual split images 12A, 12A of the adjacentlight sources 12, 12 may overlap.

FIG. 4 is a graph showing a front luminance distribution given by lightemitted from a single light source 12 after transmitting through theoptical element 15 and before entering the diffuser plate 14.

As shown in FIG. 4, the front luminance distribution shows anear-triangle profile maximized in the luminance level at a positionstraightly above the light source 12, and sloping down towards thepositions straightly above the adjacent light sources 12. The frontluminance distribution shown in FIG. 4 is slightly deformed as comparedwith a front luminance distribution having a triangle profile, whereinsuch deformation is ascribable to action of light reflected on thereflective plate 13.

Profile of the front luminance distribution obtained immediately afterbeing emitted from the light source 12 is not limited to the triangleprofile, but may also be a near-triangle profile with a rounded apex(see FIG. 5), profile having shoulders on the inclined portions thereof(see FIG. 6), a profile having step-wisely varied slope on the inclinedportions (see FIG. 7), and so forth.

FIG. 8 is a graph showing front luminance distribution of light beforetransmitting through a diffuser plate 14 under varied distance W, forthe case where the split images 12A, 12A, . . . of the plurality oflight sources 12, 12, . . . overlap, collectively showing a frontluminance distribution observed under a designed distance W, and frontluminance distributions observed under ±8% shift from the distance W.

The front luminance distributions shown in FIG. 8 express resultsobtained by the Monte Carlo simulation of light emitted from the lightsources 12, 12, . . . reflected, refracted and scattered by thereflective plate 13 and the optical element 15, conforming toprobabilities according to the optical characteristics.

In FIG. 8, every single light source 12 has a front luminancedistribution maximized at the position straightly above the light source12, and sloping down towards the positions straightly above the adjacentother light sources, wherein at the middle point between two adjacentlight sources 12, 12, the split images 12A, 12A of two these lightsources 12, 12 overlap, and parts of the individual front luminancedistributions overlap.

If the split images 12A, 12A do not overlap, width of trail (width inthe direction of arrangement of the light sources 12, 12, . . . ) of thefront luminance distribution of the individual light sources 12, 12, . .. may fluctuate, when the distance W between the light sources 12 andthe optical element 15 varied, and thereby the front luminancedistribution may largely vary. For example, when the distance W becomeslarger than the designed distance W, the width of trail of the frontluminance distribution of the individual light sources 12, 12, . . .overlap, and on the contrary when the distance W becomes smaller thanthe designed distance W, the luminance level decreases at a point(middle point) between every adjacent light sources 12, 12, . . . ,largely modifying the front luminance distribution.

In contrast, in the surface emission device 10, the split images 12A,12A, . . . of the light sources 12, 12, . . . preliminarily overlapunder the designed distance W, and part of the individual frontluminance distributions overlap with each other, so that fluctuation inthe luminance level relative to changes in the distance W between thelight sources 12, 12, . . . and the optical element 15 may besuppressed, and as shown in FIG. 8, changes in the front luminancedistribution may be small even if the distance W changes, and therebynon-uniformity in luminance may be suppressed.

In addition, because the non-uniformity in luminance ascribable tochanges in the distance W between the light sources 12, 12, . . . andthe optical element 15 may be suppressed, the degree of freedom in thearrangement of the optical element 15 relative to the housing 11 may beimproved, and thereby workability in the process of assembling theindividual components may be improved.

Moreover, overlapping of the split images 12A, 12A, . . . of the lightsources 12, 12, . . . is synonymous to widening of the width of trail ofthe front luminance distribution, and this raises a property of makingthe front luminance distribution per se less susceptible to changes inthe distance W.

FIG. 9 is a graph showing front luminance distribution of light beforetransmitting through a diffuser plate 14 under varied distance W, for acase where the split images 12A, 12A, . . . of the light sources 12, 12,. . . slightly overlap at the middle point of between the light sources12, 12, collectively showing a front luminance distribution observedunder a designed distance W, and front luminance distributions observedunder ±8% shift from the distance W.

The front luminance distributions shown in FIG. 9 express resultsobtained by the Monte Carlo simulation for the case of reflection,refraction and scattering conforming to probabilities according to theoptical characteristics, similarly to as shown in FIG. 8.

Also for the case where the split images 12A, 12A, . . . of the lightsources 12, 12, . . . slightly overlap as shown in FIG. 9, it wasconfirmed that fluctuation in the luminance level relative to changes inthe distance W between the light sources 12, 12, . . . and the opticalelement 15 may be suppressed, and that changes in the distance Wresulted in only small changes in the front luminance distribution, sothat non-uniformity in luminance may be suppressed. As a consequence, asdescribed in the above, the degree of freedom in designing the distanceW may be improved, by virtue of overlapping of the split images 12A,12A, . . . of the light sources 12, 12, . . . , and spreading of thewidth of trail of the front luminance distribution correlative tospreading of the split images 12A, 12A, . . . .

Paragraphs below will show specific examples of configuration of thesurface emission device 10, capable of suppressing non-uniformity inluminance (see FIG. 10 to FIG. 21).

In general, in thin-type liquid crystal display devices, the diameter Dof the light sources (cold cathode fluorescent lamps) is 3.0 mm to 4.0mm, the distance L between the centers of every adjacent light sourcesis 20 mm to 40 mm, and the distance W from the center of the lightsource to the optical element in the direction of optical axis is 6.0 mmto 16.0 mm. As the optical element, engineering plastics low in priceand adapted to mass production are used, wherein the thickness d of theoptical element is 0.3 mm to 2.0 mm, and the refractive index n is 1.50to 1.63. Refractive index n₀ of air is approximately 1.0.

For example, assuming W=11.7 mm and D=3.0 mm under L=23.7 mm, as shownin FIG. 10, the split images may overlap if the travel range x=L/2−D/2of the split images of the light sources in the direction normal to theoptical axis is 10.35 mm or larger.

In this case, given with d=0.4 mm and n=1.585, the tangential angle ψ ofthe optical element and the travel range x may be in relation as shownin FIG. 11, based on the equation (1) to the equation (3). From FIG. 11,the tangential angle b giving x=10.35 mm is found to be approximately56°. As a consequence, when the parameters adoptable to the generalthin-type liquid crystal display devices are given as L=23.7 mm, W=11.7mm, D=3.0 mm, d=0.4 mm, n=1.585 and n₀=1.0, it is necessary for theluminance distribution generating layer of the optical element to have aprofile with a maximum tangential angle a equal to or larger than thetangential angle ψ=56°.

As described in the above, by determining all parameters, that is, thedistance L between the individual centers of every adjacent lightsources, the refractive index n of the optical element, the thickness dof the optical element, the distance W from the center of the lightsource to the optical element in the direction of optical axis, therefractive index n0 of air in the air layer, and the diameter D of thelight source, a profile required for the luminance distributiongenerating layer of the optical element may be determined by thetangential angle calculated using the equation (1) to equation (3).

Maximum values (b_(max)) and minimum values (b_(min)) of the tangentialangle b calculated within the ranges of L=20 mm to 40 mm, W=6.0 mm to16.0 mm, D=3.0 mm to 4.0 mm, d=0.3 mm to 2.0 mm, n=1.50 to 1.63, whichare the parameters generally adopted to the liquid crystal displaydevices, are shown in Table 1.

For an exemplary case with L/W=3.0, (L/2−D/2) shows a maximum valueunder L=40 mm, W=13.3 mm, D=3.0 mm, and a maximum value (b_(max)) isshown under n=1.50, d=0.3 mm.

TABLE 1 L/W bmin(°) bmax(°) 1.5 40 54 1.6 43 56 1.7 45 58 1.8 47 60 1.948 62 2.0 50 63 2.1 52 64 2.2 53 66 2.3 55 67 2.4 56 68 2.5 57 69 2.6 5870 2.7 59 71 2.8 60 71 2.9 61 72 3.0 61 73 3.1 62 73 3.2 63 74 3.3 63 743.4 64 75 3.5 64 75 3.6 65 76 3.7 65 76 3.8 66 76 3.9 66 77 4.0 67 77

If maximum tangential angle a larger than the tangential angle b shownin Table 1 should reside in the luminance distribution generating layer18, the split images 12A, 12A, . . . of the light sources 12, 12, . . .may overlap, so that in the surface emission device 10, the opticalelement 15 is formed so that the maximum tangential angle a larger thanthe tangential angles b shown in Table 1 may reside in the luminancedistribution generating layer 18.

Accordingly, in the surface emission device 10, the split images 12A,12A, . . . of the light sources 12, 12, . . . overlap, so that changesin the distance W from the center of the light source 12 to the opticalelement 15 in the direction of optical axis P may result in only smallchanges in the front luminance distribution, thereby the non-uniformityin luminance may be suppressed.

A more preferable front luminance distribution may be exemplified by acase shown in FIG. 12, in which split image 12A reaches the positionstraightly above both adjacent light sources 12, 12. In order to obtainthis sort of front luminance distribution, the tangential angle ψsatisfying x=L−D/2 may be the maximum tangential angle a, so that it isgood enough that the tangential angle c under which the split image 12Aof the light source 12 reaches the center of the adjacent light source12 may agree with the maximum tangential angle a. It is to be noted thatstraight line T shown in FIG. 12 represents the front luminancedistribution obtained by summing up the front luminance distributions ofthe individual light sources 12, 12, . . . .

Table 2 shows maximum values (c_(max)) and minimum values (c_(min)) ofthe tangential angle c using the parameters same as those used forcalculating the values in Table 1, including L=20 mm to 40 mm, W=6.0 mmto 16.0 mm, D=3.0 mm to 4.0 mm, d=0.3 mm to 2.0 mm, and n=1.50 to 1.63.

TABLE 2 L/W Cmin(°) Cmax(°) 1.5 61 73 1.6 63 74 1.7 64 75 1.8 65 76 1.966 76 2.0 67 77 2.1 67 78 2.2 68 78 2.3 68 78 2.4 69 79 2.5 69 79 2.6 7080 2.7 70 80 2.8 70 80 2.9 71 80 3.0 71 81 3.1 71 81 3.2 71 81 3.3 72 813.4 72 81 3.5 72 81 3.6 72 82 3.7 72 83 3.8 72 84 3.9 72 84 4.0 72 84

It may therefore be said that, if the maximum tangential angle a same asthe tangential angle c shown in Table 2 should reside in the luminancedistribution generating layer 18, the split images 12A, 12A, . . . ofthe light sources 12, 12, . . . may overlap over the entire rangebetween every adjacent light sources 12, 12, . . . .

In addition, in order to obtain the front luminance distribution shownin FIG. 12, it may be necessary that, assuming the luminance level atthe position straightly above the light source 12 as 1, the luminancelevel of the split image 12A of this light source 12 at the middle pointbetween itself and the adjacent light source 12 is approximately halvedto as low as 0.4 to 0.6 or around, and the luminance level at theposition straightly above the adjacent light source 12 is approximately0. Accordingly, it may be necessary that the maximum tangential angle aof the optical element 15 is approximately same with the tangentialangle c shown in Table 2, and that the luminance distribution generatinglayer 18 contains portions with a tangential angle of b or larger andsmaller than c to as much as 40% to 60%. The tangential angle b is anangle under which the split image 12A of the light source 12 reachesL/2, as described in the above, and the tangential angle c is an angleunder which the split image 12A of the light source 12 reaches L.

In the surface emission device 10, the optical element 15 is formed sothat the maximum tangential angle a almost equal to the tangential anglec such as shown in Table 2 resides in the luminance distributiongenerating layer 18, and that the portions with a tangential angle of bor larger and smaller than c are contained to as much as 40% to 60% inthe optical luminance distribution generating layer 18.

Accordingly, in the surface emission device 10, the split images 12A,12A, . . . of the light sources 12, 12, . . . overlap over the entireregion between the individual light sources 12, 12, . . . , so thatchanges in the distance W from the center of the light source 12 to theoptical element 15 in the direction of optical axis P may result in onlysmall changes in the front luminance distribution, thereby thenon-uniformity in luminance may be suppressed.

FIG. 13 is a graph showing a relation between the maximum tangentialangle a and the travel range x of the split image, assuming the distanceW from the center of the light source to the optical element in thedirection of optical axis as 1, the diameter D of light source as 0.25,giving W/D=4, the refractive index n of the optical element as 1.585,and the thickness d of the optical element as 0.4 mm.

As shown in FIG. 13, rate of change of the maximum tangential angle aincreases as the travel range x increases. Since increase in L/W,expressing a ratio of the distance L between every adjacent lightsources with respect to the distance W from the center of the lightsource to the optical element in the direction of optical axis, resultsin increase also in the travel range x, so that increase in L/W resultsin increase in the amount of change of travel range x relative to changein the maximum tangential angle a.

As described above, the increase in the rate of change of maximumtangential angle a makes formation of the luminance distributiongenerating layer difficult. Accordingly, increase in L/W makes formationof the luminance distribution generating layer difficult, andconsequently makes control of the maximum tangential angle a difficult.

The maximum tangential angle a may be controllable in the range of L/Wof 2.5 or smaller, so that non-uniformity in luminance may appropriatelybe suppressed in the range of Table 2 with L/W of 2.5 or smaller.

FIG. 14 and FIG. 15 are graphs showing front luminance distributions inthe states where light emitted from the light source 12 transmittedthrough the optical element 15 and the diffuser plate 14. FIG. 14 is agraph corresponding to a front luminance distribution when the designeddistance W shown in FIG. 8 is kept, and FIG. 15 is a graph correspondedto a front luminance distribution when the designed distance W shown inFIG. 9 is kept.

As shown in FIG. 14 and FIG. 15, the front luminance distribution ismade almost uniform, in the state of light after being transmittedthrough the diffuser plate 14 by virtue of diffusing function of thediffuser plate 14.

By using the diffuser plate 14 in this way, the front luminancedistribution may be made uniform, and the non-uniformity in luminancemay be prevented from occurring.

As described in the above, since the front luminance distribution may bemade uniform by using the diffuser plate 14, in the state of lightemitted from the light sources 12, 12, . . . and before beingtransmitted through the diffuser plate 14, the front luminancedistribution may be made uniform if large difference between the maximumvalues and the minimum values of the luminance in the front luminancedistribution is avoidable.

An allowable range of ratio of the maximum values and the minimum valuesof the luminance level, under which the front luminance distribution maybe made uniform by the action of the diffuser plate 14, may be 0.7 orlarger, for example, taking the action of the diffuser plate intoconsideration.

FIG. 16 and FIG. 17 are graphs plotting on the ordinate the tangentialangle Ψ, and plotting on the abscissa the ratio of content of suchtangential angle Ψ in the luminance distribution generating layer,obtained when 23 samples in total were investigated into the state ofnon-uniformity in luminance.

FIG. 16 and FIG. 17 are graphs, showing data similarly as in FIG. 13,expressing relations between the tangential angle ψ and the ratio ofsuch tangential angle ψ, assuming the distance W from the center of thelight source to the optical element in the direction of optical axis as1, the diameter D of light source as 0.25, giving W/D=4, the refractiveindex n of the optical element as 1.585, and the thickness d of theoptical element as 0.4 mm. Note that a ratio of the distance L betweenthe centers of every adjacent light sources relative to the distance Wherein is given as L/W=2.0, and transmissivity of light of the diffuserplate is 60%.

FIG. 16 shows data of 11 samples (A to K) having ratios of the maximumvalues and the minimum values of the luminance level in the frontluminance distribution of light before being transmitted through thediffuser plate of 0.7 or larger, causative of only small incidence ofnon-uniformity in luminance, and therefore ensured with desirableuniformity in the front luminance distribution.

On the other hand, FIG. 17 shows data of 12 samples (L to W) havingratios of the maximum values and the minimum values of the luminancelevel in the front luminance distribution of light before beingtransmitted through the diffuser plate of smaller than 0.7, causative oflarge incidence of non-uniformity in luminance, and therefore failed inensuring desirable uniformity in the front luminance distribution.

As shown in FIG. 16, data corresponding to small incidence ofnon-uniformity in luminance indicate that all samples contain theportions with the tangential angle ψ larger than the tangential angleb=56° in the luminance distribution generating layer, and that theportions with the tangential angle b (=56°) are contained approximatelyto as much as 10% to 30% of all tangential angles ψ (indicated by R inFIG. 16).

On the other hand, the data corresponding to large incidence ofnon-uniformity in luminance shown in FIG. 17 involves samples (L, M, N,O, P, Q) having the maximum tangential angle a smaller than thetangential angle b (=56°), samples (T, V, W) having portions with thetangential angle b or larger contained to as much as exceeding 30%, anda sample (R) having portions with the tangential angle b only to as muchas less than 10%, excluding 2 samples.

As shown in FIG. 16 and FIG. 17, it was confirmed that thenon-uniformity in luminance was suppressed, when the portions with thetangential angle b (=56°) were contained to as much as 10% to 30% of alltangential angles ψ, and the ratio of maximum values and the minimumvalues of the luminance level in the front luminance distribution oflight before being transmitted through the diffuser plate consequentlybecame 0.7 or larger. As a consequence, the non-uniformity in luminancemay be suppressed, by forming the luminance distribution generatinglayer 18 of the optical element 15 so as to contain the portions withthe tangential angle b or larger to as much as 10% to 30% of thetangential angles ψ.

FIG. 18 is a graph showing a front luminance distribution observed in astate where light is emitted from the light sources transmitted throughthe optical element 15 and luminance distribution generating layer 18.As shown in FIG. 18, when the split image 12A of the light source 12 ispositioned straightly above the adjacent light source 12 (see FIG. 12),uniformity in the front luminance distribution may be ensured even ifthe diffuser plate 14 is not provided. It is necessary herein,particularly for the case where L/W has large values, to form theluminance distribution generating layer 18 with large tangential anglesψ, for example with a tangential angle b of 56° or larger, in a highlyprecise manner.

However, as described in the above, by providing the diffuser plate 14capable of diffusing light transmitted through the optical element 15,the split image 12A may be positioned straightly above the adjacentlight source 12 by virtue of the action of the diffuser plate 14, in thestate of light after being transmitted through the diffuser plate, evenif the split image 12A of the light source 12 does not positionstraightly above the adjacent light source 12 in the state of lightbefore being transmitted through the diffuser plate 14. As aconsequence, if the diffuser plate 14 is provided, it will be not somuch necessary to form the luminance distribution generating layer 18with large tangential angles ψ irrespective of magnitude of L/W, andthereby manufacturing of the optical element 15 may be facilitated.

For the case where the diffuser plate 14 is not provided, the outersurface of the structural portions 18 a, 18 a, . . . of the luminancedistribution generating layer 18 of the optical element 15 maypreferably be formed into curved profile, in order to consecutivelyoverlap the split images 12 a of the light source 12 with each other,whereas for the case where the diffuser plate 14 is provided, the travelrange x of the split image 12A may be reduced, and a smooth luminancedistribution may be formed by virtue of effects of the diffuser plate 14even under discontinuous split images 12A, so that the outer surface ofthe structural portions 18 a, 18 a, . . . may now be formed into apolygonal profile, or as having flat surface in part of the outersurface thereof, for example, and thereby manufacturing of the opticalelement 15 may be facilitated.

FIG. 19 shows an exemplary optical element 15 having structural portions18 a, 18 a . . . formed into a flat plane at least in part thereof, whenthe diffuser plate 14 is provided.

FIG. 19 shows an exemplary case where a structural component is composedof a set of three structural portions 18 b, 18 c, 18 d, and a largenumber of such structural components are consecutively formed.

In the example shown in FIG. 19, given with L/W=2.0, the luminancedistribution generating layer 18 contains the portions with a tangentialangle b of 56° or larger to as much as 10% to 15%, the luminancedistribution generating layer 18 contains the portions with a tangentialangle of 0°, that is, the portions formed into a flat plane normal tothe optical axis, to as much as 10% to 20%, and the structural portion18 c and the structural portion 18 d are formed into polygonal profiles.

FIG. 20 is a graph plotting on the ordinate the tangential angle ψ, andplotting on the abscissa the ratio of content of such tangential angle ψin the luminance distribution generating layer 18, obtained for theoptical element 15 shown in FIG. 19. As shown in FIG. 20, the opticalelement 15 shown in FIG. 19 contains the portions with a tangentialangle of approximately 56° in the luminance distribution generatinglayer 18 to as much as 10% to 15%.

FIG. 21 is a graph showing a front luminance distribution in a statewhere light emitted from the light sources 12, 12, . . . transmittedthrough the diffuser plate 14, for the cases shown in FIG. 19 and FIG.20. Transmissivity of light of the diffuser plate 14 herein is 60%. Asshown in FIG. 21, it was confirmed that the light was diffused by thediffusive action of the diffuser plate 14, a desirable level ofuniformity in the front luminance distribution was ensured, and therebythe non-uniformity in luminance was suppressed.

Accordingly, the non-uniformity in luminance may be suppressed by usingthe diffuser plate 14, even when the outer surface of the structuralportions 18 a, 18 a, . . . of the luminance distribution generatinglayer 18 of the optical element 15 was formed into a polygonal profile,or partially into a flat plane.

In the surface emission device 10, since the optical element component16 such as diffusion sheet, prism sheet, or reflective polarizer, forexample, is disposed as being opposed to the optical element 15 acrossthe diffuser plate 14, the light diffused by the diffuser plate 14 mayfurther be subjected to diffusion, scattering and so forth by theoptical element component 16, and thereby the suppressive effect on thenon-uniformity in luminance may be improved.

Next, an optical element package, which is a structure of integratingthe optical element 15 and the diffuser plate 14, will be explained (seeFIG. 22 and FIG. 23).

As described in the above, in the surface emission device 10, theoptical element 15, the diffuser plate 14 and the optical elementcomponent 16 are sequentially disposed as viewed from the side of thelight sources 12, 12, . . . , wherein warping, waving or the likebecause of its low rigidity may occur due to the thickness of thesecomponents, raising a cause for generating non-uniformity in luminance.

In order to prevent such warping and waving from occurring, the opticalelement 15 and the diffuser plate 14, or the optical element 15 and thediffuser plate 14 and the optical element component 16 may be packagedusing a packaging component 20 such as transparent sheet or transparentfilm, to thereby configure an optical element package 21 (see FIG. 22).

Alternatively, for example, the optical element 15 and the diffuserplate 14 may be bonded using a ultraviolet-curable resin orpressure-sensitive adhesive, to thereby configure an optical elementpackage 22 (see FIG. 23). In this case, in addition to the opticalelement 15 and the diffuser plate 14, also the optical element component16 may be bonded to the diffuser plate 14, to thereby configure theoptical element package 22.

By configuring the optical element package 21 or the optical elementpackage 22, the rigidity may be enhanced by increasing the thickness,and thereby avoiding the warping, waving and so forth.

Paragraphs below will show exemplary sectional profiles of the luminancedistribution generating layer 18 of the optical element 15 (see FIG. 24to FIG. 29).

Although the non-uniformity in luminance may be suppressed by formingthe sectional profile (profile of the outer surface) of the luminancedistribution generating layer 18 of the optical element 15 into adesired curved profile, it may often be difficult to form the luminancedistribution generating layer 18 into the curved profile as described inthe above. Formation of the luminance distribution generating layer 18with polygonal profiles such as shown below, as approximation of thecurved profile, will now successfully suppress the non-uniformity inluminance, while keeping the desirable workability.

FIG. 24 shows an example 100 of the luminance distribution generatinglayer 18 having such polygonal profile.

The luminance distribution generating layer 100 is configured by anouter surface 101 laid in parallel with the direction of arrangement ofthe light sources, and the outer surfaces 102, 102, 103, 103, . . . ,107, 107 gradually increased, referring to the outer surface 101, in theangle of inclination with respect to the direction of arrangement of thelight sources towards the light sources. The luminance distributiongenerating layer 100 has a profile symmetrical in the direction ofarrangement of the light sources about a center line M which falls onthe point halving the outer surface 101. Assuming now angles ofinclination of the individual outer surfaces 101, 102, 103, . . . in thedirection of arrangement of the light sources sequentially as s1, s2,s3, . . . , s7, the luminance distribution generating layer 100 isformed so as to satisfy s1<s2<s3< . . . <s7.

Although the luminance distribution generating layer 100 herein isconfigured with 13 outer surfaces (line segments) differed in the angle,the number of outer surfaces is not limited to 13, instead, the numberof outer surfaces may arbitrarily be determined while considering thedistance L between the light sources, the diameter D of the light sourceand so forth.

By using the luminance distribution generating layer 18 having thesectional profile approximated to a curved profile as shown in FIG. 24,it is no more necessary to form such curved profile which may otherwisebe difficult to form, and thereby ensuring a desirable workability ofthe optical element.

FIG. 25 and FIG. 26 show examples 200, 300 of the luminance distributiongenerating layer, wherein the polygonal profile shown in FIG. 24 wasdivided to form a plurality of structural portions.

The luminance distribution generating layer 200 shown in FIG. 25 isconfigured with a plurality of sets of two structural portions 200 a,200 b alternately arranged.

The structural portion 200 a has seven outer surfaces, for example, andis composed of outer surfaces 201, 202, 202, 203, 203, 204, 204, whereasthe structural portion 200 b also has seven outer surfaces, for example,and is composed of outer surfaces 205, 206, 206, 207, 207, 208, 208.

The outer surfaces 201, 205 are laid in parallel with the direction ofarrangement of the light sources, and respectively have an angle ofinclination same as the angle of inclination s1 of the luminancedistribution generating layer 100. The angles of inclination of theouter surfaces 202, 203, 204 with respect to the direction ofarrangement of the light sources are respectively set equal to theangles of inclination s3, s5, s7 in the luminance distributiongenerating layer 100, and the angles of inclination of the outersurfaces 206, 207, 208 with respect to the direction of arrangement ofthe light sources are respectively set equal to the angles ofinclination s2, s4, s6 in the luminance distribution generating layer100.

By using such luminance distribution generating layer 200 composed ofthe structural portions 200 a, 200 b, 200 a, 200 b, . . . derived bydivision from the profile of the luminance distribution generating layer100, the optical element may readily be processed, by virtue ofsmallness in the number of outer surfaces of the structural portions 200a, 200 b.

The luminance distribution generating layer 300 shown in FIG. 26 isconfigured with a plurality of sets of two structural portions 300 a,300 b alternately arranged.

The structural portion 300 a has six outer surfaces, for example, and iscomposed of outer surfaces 301, 301, 302, 302, 303, 303, whereas thestructural portion 300 b also has six outer surfaces, for example, andis composed of outer surfaces 304, 304, 305, 305, 306, 306.

The angles of inclination of the outer surfaces 301, 302, 303 withrespect to the direction of arrangement of the light sources arerespectively set equal to the angles of inclination s3, s5, s7 in theluminance distribution generating layer 100, and the angles ofinclination of the outer surfaces 304, 305, 306 with respect to thedirection of arrangement of the light sources are respectively set equalto the angles of inclination s2, s4, s6 in the luminance distributiongenerating layer 100.

Between the structural portions 300 a and 300 b, there is formed aparallel plane 307 which is parallel with the direction of arrangementof the light sources. The parallel plane 307 is a plane corresponding tothe outer surface 101 of the luminance distribution generating layer100.

By using such luminance distribution generating layer 300 composed ofthe structural portions 300 a, 300 b, 300 a, 300 b, . . . derived bydivision from the profile of the luminance distribution generating layer100, the optical element may readily be processed, by virtue ofsmallness in the number of outer surfaces of the structural portions 300a, 300 b.

Furthermore, for the case of using the luminance distribution generatinglayer 300, when the optical element is formed by injection molding usinga die 1000 such as shown in FIG. 27, the die 1000 will have a projectionbetween the portions for forming the structural portion 300 a and thestructural portion 300 b, so that the die is added with a large rigidityby virtue of the projection 1001 having a predetermined width in thedirection of arrangement of the light sources. Accordingly, theprojection 1001 may be less likely to deform, may allow smooth releasingof the die 1000, and may thereby improve accuracy of processing of themolded luminance distribution generating layer 300.

FIG. 28 and FIG. 29 show examples 400, 500 of the luminance distributiongenerating layer, wherein the polygonal profile was divided into three.

The luminance distribution generating layer 400 shown in FIG. 28 isconfigured with a plurality of sets of three structural portions 400 a,400 b, 400 c alternately arranged.

The structural portions 400 a, 400 b, 400 c respectively have five outersurfaces, for example, wherein the angles of inclination of the outersurfaces 401, 402, 403 of the structural portion 400 a with respect tothe direction of arrangement of the light sources are respectively setequal to the angles of inclination s1, s3, s6 in the luminancedistribution generating layer 100, the angles of inclination of theouter surfaces 404, 405, 406 of the structural portion 400 b withrespect to the direction of arrangement of the light sources arerespectively set equal to the angles of inclination s1, s4, s7 in theluminance distribution generating layer 100, and the angles ofinclination of the outer surfaces 407, 408, 409 of the structuralportion 400 c with respect to the direction of arrangement of the lightsources are respectively set equal to the angles of inclination s1, s2,s5 in the luminance distribution generating layer 100.

By using such luminance distribution generating layer 400 composed ofthe structural portions 400 a, 400 b, 400 c, derived by division fromthe profile of the luminance distribution generating layer 100, theoptical element may readily be processed, by virtue of smallness in thenumber of outer surfaces of the structural portions 400 a, 400 b, 400 c.

The luminance distribution generating layer 500 shown in FIG. 29 isconfigured with a plurality of sets of three structural portions 500 a,500 b, 500 c alternately arranged.

The structural portions 500 a, 500 b, 400 c respectively have four outersurfaces, for example, wherein the angles of inclination of the outersurfaces 501, 502 of the structural portion 500 a with respect to thedirection of arrangement of the light sources are respectively set equalto the angles of inclination s3, s6 in the luminance distributiongenerating layer 100, the angles of inclination of the outer surfaces503, 504 of the structural portion 500 b with respect to the directionof arrangement of the light sources are respectively set equal to theangles of inclination s4, s7 in the luminance distribution generatinglayer 100, and the angles of inclination of the outer surfaces 505, 506of the structural portion 500 c with respect to the direction ofarrangement of the light sources are respectively set equal to theangles of inclination s2, s5 in the luminance distribution generatinglayer 100.

Between the structural portions 500 a, 500 b, 500 c, there are formedparallel planes 507, 507 which are parallel with the direction ofarrangement of the light sources. The parallel planes 507, 507 areplanes corresponding to the outer surface 101 of the luminancedistribution generating layer 100.

By using such luminance distribution generating layer 500 composed ofthe structural portions 500 a, 500 b, 500 c derived by division from theprofile of the luminance distribution generating layer 100, the opticalelement may readily be processed, by virtue of smallness in the numberof outer surfaces of the structural portions 500 a, 500 b, 500 c.

Also for the case where the luminance distribution generating layer 500is used, a die will have a highly rigid projection similarly to the casewhere the luminance distribution generating layer 300 was used, andthereby accuracy of processing of the molded luminance distributiongenerating layer 500 may be improved.

The descriptions in the above showed the exemplary luminancedistribution generating layers having a plurality of sets of two orthree structural portions sequentially arranged, wherein the number ofdivision of the polygonal profile is not limited to two or three, butmay be four or more. These structures may be understood as beingobtained by dividing a polygonal profile into a plurality of structuralportions, showing optical characteristics not so largely differ fromthose of the undivided luminance distribution generating layer 100, sothat the structure may arbitrarily be selected considering theprocessability.

FIG. 30 is a graph showing exemplary results of simulation of frontluminance distribution of the optical element having the luminancedistribution generating layer 300, and corresponds to FIG. 4.

The front luminance distribution shows a mountain-like profile maximizedin the luminance level at the position straightly above the light source12, and sloped down towards the positions straightly above adjacentother light sources.

FIG. 31 is a graph showing a front luminance distribution observed whenall light sources were turned on in FIG. 30, and corresponds to FIG. 18.

The results shown in FIG. 30 and FIG. 31 are found to contain slightnon-uniformity in luminance as a whole, when compared with the resultsshown in FIG. 4 and FIG. 18, but the non-uniformity in luminance isdifferent from non-uniformity in light sources depending on the distanceL between the light sources, and may be suppressed to a non-problematiclevel in practice, by disposing a diffuser plate, diffuser sheet or thelike.

All of the specific profiles and structures of the individual componentsshown above in the preferred modes of embodiment are merely part ofexamples of embodiment of the present invention, by which the technicalscope of the present invention should never be interpreted in a limitedmanner.

1-52. (canceled) 53: A surface emission device having a plurality oflight sources respectively shaped into a columnar form extending in apredetermined direction and disposed on the same plane as being extendedin the same direction; an optical element having transparency andhaving, as formed therein, a luminance distribution generating layersuppressing variation, in a direction of optical axes, in luminance oflight emitted from the plurality of light sources; and a reflectivesurface positioned as being opposed to the optical element across theplurality of light sources, while keeping an air layer between theoptical element and itself, and reflecting light emitted from the lightsources, wherein the luminance distribution generating layer of theoptical element being composed of a plurality of structural portionsextending in a longitudinal direction of the light sources andprojecting in the direction of optical axes, the surface emission devicecharacterized by: having the optical element containing the maximumtangential angle a which satisfies x>L/2−D/2 and configured such that acomponent in an arrangement direction of the structural portions asviewed in a sectional profile thereof at an outer surface section in thesectional profile of a structural portion having a tangential angle Ψthat is larger than or equal to a tangential angle b of 56° has apercentage of 10% to 30% with respect to a component in the arrangementdirection of the structural portions as viewed in the sectional profilethereof at an outer surface in the sectional profile of a structuralportion included in the luminance distribution generating layer, whentravel range x of a split image of the light sources in the directionnormal to the optical axes is calculated using conditional equation (1)to conditional equation (3) below:n ₀ sin(a)=n sin(a−θ ₂)  (1)n₀ sin θ₁=n sin θ₂  (2)x=W tan θ₁ +d tan θ₂  (3), assuming: distance between centers of everyadjacent light sources as L; refractive index of the optical element asn; thickness of the optical element as d; distance from the center ofthe light sources to the optical element in the direction of opticalaxes as W; refractive index of air in the air layer as n₀; angle ofincidence of light emitted from the light sources and coming into theoptical element, relative to the direction of optical axes, as θ₁; angleof refraction of light, incident on the optical element, in the opticalelement as θ₂; diameter of each light source as D; angles formed betweena tangential line in contact with an outer surface of the luminancedistribution generating layer and a plane orthogonal to the opticalaxes, as viewed in the sectional profile orthogonal to the longitudinaldirection of the structural portions of the luminance distributiongenerating layer, as tangential angles Ψ; a tangential angle largest ofall tangential angles Ψ as a maximum tangential angle a; a tangentialangle, out of all the tangential angles Ψ, under which the split imageof the light source reaches L/2 as b; and L/W is 1.9 to 3.5. 54: Thesurface emission device as claimed in claim 53, characterized in thatthe plurality of structural portions included in the luminancedistribution generating layer have the same size and shape. 55: Thesurface emission device as claimed in claim 53, characterized by havingthe optical element containing maximum tangential angle “a” whichsatisfies x=L−D/2. 56: The surface emission device as claimed in claim53, characterized in that a diffuser plate is disposed as being opposedto the light sources across the optical element. 57: The surfaceemission device as claimed in claim 53, characterized in that: adiffuser plate is disposed as being opposed to the light sources acrossthe optical element, and an optical element package formed by packagingthe diffuser plate and the optical element with a packaging component isprovided. 58: The surface emission device as claimed in claim 57,characterized in that at least one additional optical element besidesthe above-described optical element is provided within the opticalelement package. 59: The surface emission device as claimed in claim 53,characterized in that: a diffuser plate is disposed as being opposed tothe light sources across the optical element, and an optical elementpackage composed by bonding the diffuser plate and the optical elementis provided. 60: The surface emission device as claimed in claim 53,characterized in that an outer surface of the individual structuralportions of the luminance distribution generating layer is shaped into acurved profile. 61: The surface emission device as claimed in claim 53,characterized in that an outer surface of the individual structuralportions of the luminance distribution generating layer is shaped into apolygonal profile. 62: The surface emission device as claimed in claim61, characterized in that the individual structural portions are shapedinto a form symmetrical about the line in the direction of arrangementof the light sources, and shaped so that the angle of inclination of theindividual outer surfaces thereof with respect to the direction ofarrangement of the light sources gradually increases as being closer tothe light sources. 63: The surface emission device as claimed in claim62, characterized in that a flat plane orthogonal to the optical axis isformed between every adjacent structural portions. 64: The surfaceemission device as claimed in claim 53, characterized in that a basematerial and the luminance distribution generating layer are integrated.65: The surface emission device as claimed in claim 53, characterized inthat: a base material and the luminance distribution generating layerare composed of different materials, and the luminance distributiongenerating layer is bonded to the base material. 66: The surfaceemission device as claimed in claim 65, characterized in that: the basematerial is composed of polyethylene terephthalate, and the luminancedistribution generating layer is composed of ultraviolet curable resin.67: An optical element configured as having formed therein a luminancedistribution generating layer suppressing variation, in a direction ofoptical axes, in luminance of light emitted from a plurality of lightsources respectively shaped into a columnar form extending in apredetermined direction and disposed on the same plane as being extendedin the same direction, in which the luminance distribution generatinglayer is composed of a plurality of structural portions extending in alongitudinal direction of the light sources and projecting in thedirection of optical axes, the optical element characterized by beingconfigured so as to contain a maximum tangential angle a which satisfiesx>L/2−D/2 and configured such that a component in an arrangementdirection of the structural portions as viewed in a sectional profilethereof at an outer surface section in the sectional profile of astructural portion having a tangential angle Ψ that is larger than orequal to a tangential angle b of 56° has a percentage of 10% to 30% withrespect to a component in the arrangement direction of the structuralportions as viewed in the sectional profile thereof at an outer surfacein the sectional profile of a structural portion included in theluminance distribution generating layer, when travel range x of a splitimage of the light sources in a direction normal to the optical axes iscalculated using conditional equation (1) to conditional equation (3)below:n ₀ sin(a)=n sin(a−θ ₂)  (1)n₀ sin θ₁=n sin θ₂  (2)x=W tan θ₁ +d tan θ₂  (3) assuming: distance between the centers ofevery adjacent light sources as L; refractive index of the opticalelement as n; thickness of the optical element as d; distance from thecenter of the light sources to the optical element in the direction ofoptical axes as W; refractive index of air in the air layer as n₀; angleof incidence of light emitted from the light sources and coming into theoptical element, relative to the direction of optical axes, as θ₁; angleof refraction of light, incident on the optical element, in the opticalelement as θ₂; diameter of each light source as D; angles formed betweena tangential line in contact with an outer surface of the luminancedistribution generating layer and a plane orthogonal to the opticalaxes, as viewed in the sectional profile orthogonal to a longitudinaldirection of the structural portions of the luminance distributiongenerating layer, as tangential angles Ψ; a tangential angle largest ofall tangential angles Ψ as the maximum tangential angle a; a tangentialangle, out of all the tangential angles Ψ, under which the split imageof the light source reaches L/2 as b; and L/W is 1.9 to 3.5. 68: Theoptical element as claimed in claim 67, characterized in that theplurality of structural portions included in the luminance distributiongenerating layer have the same size and shape. 69: The optical elementas claimed in claim 67, characterized in that a base material and theluminance distribution generating layer are integrated. 70: The opticalelement as claimed in claim 67, characterized in that: a base materialand the luminance distribution generating layer are composed ofdifferent materials, and the luminance distribution generating layer isbonded to the base material. 71: The optical element as claimed in claim70, characterized in that: the base material is composed of polyethyleneterephthalate, and the luminance distribution generating layer iscomposed of ultraviolet curable resin. 72: A liquid crystal displaydevice having a plurality of light sources respectively shaped into acolumnar form extending in a predetermined direction and disposed on thesame plane as being extended in the same direction; an optical elementhaving, transparency and having, as formed therein, a luminancedistribution generating layer suppressing variation, in a direction ofoptical axes, in luminance of light emitted from the plurality of lightsources, the luminance distribution generating layer being composed of aplurality of structural portions extending in a longitudinal directionof the light sources and projecting in the direction of optical axes; areflective surface positioned as being opposed to the optical elementacross the plurality of light sources, while keeping an air layerbetween the optical element and itself, and reflecting light emittedfrom the light sources; and a liquid crystal panel allowing thereonimage display and irradiated with light emitted from the plurality oflight sources, the liquid crystal display device characterized by havingthe optical element containing a maximum tangential angle “a” whichsatisfies x>L/2−D/2 and configured such that a component in anarrangement direction of the structural portions as viewed in asectional profile thereof at an outer surface section in the sectionalprofile of a structural portion having a tangential angle Ψ that islarger than or equal to a tangential angle b of 56° has a percentage of10% to 30% with respect to a component in the arrangement direction ofthe structural portions as viewed in the sectional profile thereof at anouter surface in the sectional profile of a structural portion includedin the luminance distribution generating layer, when travel range x of asplit image of the light sources in a direction normal to the opticalaxes is calculated using conditional equation (1) to conditionalequation (3) below:n ₀ sin(a)=n sin(a−θ ₂)  (1)n₀ sin θ₁=n sin θ₂  (2)x=W tan θ₁ +d tan θ₂  (3) assuming: distance between centers of everyadjacent light sources as L; refractive index of the optical element asn; thickness of the optical element as d; distance from the center ofthe light sources to the optical element in the direction of opticalaxes as W; refractive index of air in the air layer as n₀; angle ofincidence of light emitted from the light sources and coming into theoptical element, relative to the direction of optical axes, as θ₁; angleof refraction of light, incident on the optical element, in the opticalelement as θ₂; diameter of each light source as D; angles formed betweena tangential line in contact with an outer surface of the luminancedistribution generating layer and a plane orthogonal to the opticalaxes, as viewed in the sectional profile orthogonal to the longitudinaldirection of the structural portions of the luminance distributiongenerating layer, as tangential angles Ψ; a tangential angle largest ofall tangential angles Ψ as the maximum tangential angle a; a tangentialangle, out of all the tangential angles Ψ, under which the split imageof the light source reaches L/2 as b; and L/W is 1.9 to 3.5.